Kassoon

No Prep Module: Aquatic Revolution for D&D or RPGs

This adventure can be can be easily customized to a party of any size or level, or run as a level 6 adventure for 5 players. It can work as a small side adventure in an existing campaign, as a standalone one-shot, or the start of a new adventure. Use the links to the tools in their relevant section to customize the adventure to your party.

Ship Sailing

The PCs are traveling on a boat across the ocean. The players will need some form of water breathing to do this adventure, so either a spell caster with access to 3rd level Water Breathing, a scroll or potions that they find, or you can hand-wave it and make the dungeon breathable.

The boat can be one the PCs own and steer themselves, or they can book passage on one. If they go for the latter option, you can use this for the NPC captain:

Harbek Gorunn, Male Dwarf

Description: He is a husky man, who prefers to wear fine silks, though has several suits of combat armor for his hunting needs. He has done his best to style his silver hair to look like a famous performer. His amber eyes dart around the room hyper actively observing anyone and anything.
Personality: He never swears and excessively uses polite adverbs when speaking. Harbek enjoys physical pleasures, and is well known for his love of warm baths in the hot springs near the town. Voice: French accent

The ship surges through the waves across the ocean blue. A light breeze brings in the salty air, giving a small respite from the hot sun above. The travel continues on like this for several hours, with the boat rising and falling over the mostly calm waves. Later in the afternoon, the sun is obscured by the clouds in the sky, and the air becomes thicker, until eventually a heavy fog descends and obscures the area.

During their travel, the boat enters a deep fog that makes it impossible to see and navigate. A DC 15 Arcana check allows a player to find traces of a magical leyline that runs along the ocean's floor, and following the leyline will allow the boat to safely navigate the fog. Failure causes them to get lost and off-course.

Shortly after, their ship is attacked by an army of Merfolk. Play out the combat on the ship, but the PCs will quickly realize that the number of merfolk is overwhelming as crew members are killed around them and parts of the ship are set on fire and destroyed.

Eventually, their ship is sunk and the PCs are plunged into the ocean. As they sink, the PCs see a coral reef under the water, converted into a sprawling temple with tiny twinkling lights everywhere.

Coral Reef

As you sink deeper into the ocean, you can see a bright light coming from below. As it comes into view, you see a massive and brilliant coral reef along the craggy cliffs rising from the ocean floor. The reef is bright and colorful, with all sorts of bright plants and fish around the coral. Small twinkling lights appear scattered all along its surface, causing the entire structure to emit a brilliant glow that illuminates the dark ocean depths.

The entire dungeon is underwater, meaning unless PCs have a swim speed then they have disadvantage on melee attacks unless using a dagger, javelin, shortsword, spear, or trident. Ranged weapons automatically miss beyond the weapon's normal range, and have disadvantage unless it's a crossbow, net, or thrown. If the PCs lack these weapons, they can loot them from an enemy or corpse.

Coral Temple

Reef Dungeon

Enemy Patrol: 5 Gillmonkey (CR 1/4: Fifth Edition Foes p. 121), 1 Quipper (CR 0: Monster Manual p. 335), 2 Zoblin Boss (CR 1: Nerzugal's Extended Bestiary p. 97), 2 Giant Electric Catfish (CR 3: Fifth Edition Foes p. 46) [Hard, 2,060 XP rewarded] [Customize]
Chance of Encounter Per Rest: 20%

1

Weird puffballs, tall caps, and patches of fuzzy mold in a variety of colors inhabit this irregular room. In the middle of the room are descending rows of blue coral benches. Tattered red drapes cover the windows of this circular room, and a heavy curtain hangs across an archway to the east. A door next to the far wall leads to the south.

There are 3 Giant Water Beetle (CR 1/2: Fifth Edition Foes p. 25), 1 Kelpie (CR 1: Fifth Edition Foes p. 156), 2 Monstrous Crayfish (CR 2: Fifth Edition Foes p. 70) [Easy, 1,400 XP rewarded] here. [Customize]

2

Several old skeletons lie peppered near the western wall. Torn and demolished couches lie in heaps, disordered and littered about. Deep stab marks cover the hardwood furniture, and the once lush upholstery has been sliced to shreds. Above a door in the southern wall is mounted the skull of a fey. Directly across from the stained glass window stands a set of double doors in the east wall. Tattered gray drapes cover the windows of this circular room, and a heavy curtain hangs across an archway to the west.

An object in this room creates a force field.

3

Several old skeletons lie spread near the western wall. Cramped bronze gates hang on the stonework, seaweed clinging to the rusted bars. To the west and north are two alcoves filled with torn cloth and bandages. To the west, modest double doors hang slightly ajar, and a steady glowing light escapes through the crack.

There are 4 Kuo-toa Whip (CR 1: Monster Manual p. 200), 1 Marine Basilisk (CR 4: Monster Module p. 15) [Medium, 1,900 XP rewarded] here. [Customize]

4

This timeworn room is choked with seaweed and leaves broken by a separate messy passage down its middle. In the middle of the room is a wood-framed bed fitted with leather restraints. A few hungry fish make their home here, but upon your sudden arrival, they retreat to the shadows. A door stands closed to the east.

In the room is a puzzle: Each morning I appear to lie at your feet, All day I will follow no matter how fast you run, Yet I nearly perish in the midday sun. A: Shadow.

If the puzzle is solved, they find 150 gp

There are 2 Kelpie (CR 1: Fifth Edition Foes p. 156), 3 Mummy of the Deep (CR 2: Fifth Edition Foes p. 173) [Medium, 1,750 XP rewarded] here. [Customize]

5

Light fog tumbles down from above. Four beds with ragged canopies stand against opposite walls with a frayed rug lying on the floor between them. A gate of wrought iron stands in the south wall. On each side of the exit, the walls are adorned with hooks and loops that hold instruments and basic tridents in a disorganized fashion. Immense bronze gates hang on the stonework, coral clinging with cold tenacity to the rusted bars. Double doors of bronze stand closed to the north.

In this room is a trap. A door or chest is rigged to activate when opened, which activates pipes in the walls that spew hot steam.

Effect: Targets all creatures within a 20 ft. cone, DC 14 DEX save or take 30 (4d10) fire damage

Trigger: door, activates when a door or chest is opened.

Countermeasures: The DC to spot the attached wire is 15. A successful DC 15 Dexterity check using thieves' tools breaks the wire attached to the door harmlessly. A character without thieves' tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

Destroying the trap will rupture the pipes and spray boiling steam over the area. Water can't adequately douse the flames, but clay or stone (such as with Stone Shape) can be used to block the geysers. [Customize]

In the west passage is an unlocked door.

In the north passage is a locked door (DC 15). Key could be found on a nearby creature or furniture.

6

The water here is hot. coral tables lie in pieces on the floor at the north end of the room. A plain bronze door is set into the north wall, and light seeps through its cracks. On each side of the exit, a cloaked figure is draped over, and a white mace lies on the floor near its feet. A door next to the far wall leads to the south.

There are 4 Crab (CR 0: Monster Manual p. 320), 2 Sahuagin High Priest, Cybele (CR 5: Ghosts of Saltmarsh, p.251) [Deadly, 3,640 XP rewarded] here. [Customize]

7

The walls and the 25-foot-high vaulted ceiling are a sickly green color. Smashed sandstone pillars and empty armor stands are showered on the floor. Several tables stand throughout the room, weighed down by stacks of glass jars and bottles, all of them bearing labels. Helmets, shields, and a shelf of helms that bear the same crest are hung neatly on the walls. Taut iron chains extend up and down the shaft. This room has been plundered, its tables overturned. A lit hallway to the north contains a set of bronze doors, through which you hear wailing.

In the north passage is a stuck door (DC 15).

8

The room contains three curtained alcoves as well as a larger area stuffed with wine barrels. Covering the entire floor are many empty bottles. Suspended above is a seaweed-shrouded chandelier of forged iron. A lit hallway to the east contains a set of bronze doors, through which you hear a low moan.

In this room is a trap. This trap is activated when an intruder steps on one of the alternating hidden pressure plates that makes the trap swing out from a hole in the ceiling, toppling anyone in its path.

Effect: Targets all creatures within a 10 ft. square area, DC 17 DEX save or take 39 (10d10) damage and be knocked prone

Trigger: alternate tiles, activates when 20 or more pounds are placed on alternating floor tiles.

Countermeasures: A successful DC 20 Intelligence (Investigation) check will deduce that the alternating floor tiles are pressure plates, and wedging an iron spike or other object under the pressure plates prevents the trap from activating. Alternatively, step on the safe floor tiles in alternating order.

[Customize]

9

Two lanterns hang above a sturdy stone worktable in the middle of the clutter. Another door on the east wall is partially ajar, while a passage to the west leads toward a dark chamber. A dark archway leads out through the north wall.

There are 2 Giant Shark (CR 5: Monster Manual p. 328) [Hard, 3,600 XP rewarded] here. [Customize]

10

Lit by a piercing shaft of light, a pentagram stands upon a clay podium. The sides are carved with bas-reliefs of angelic figures entwined with grape vines. A lit hallway to the north contains a set of bronze doors, through which you hear murmurs. A plain bronze door is set into the west wall, and light seeps through its cracks. Six long coral tables are set with steel and glass laboratory equipment in this room. A large statue of a merfolk with its hands open and beckoning, stands before the southern wall.

There are 2 Crushing Wave Priest (CR 2: Princes of the Apocalypse p. 205), 1 Giant Moray Eel (CR 2: Fifth Edition Foes p. 91) [Easy, 1,350 XP rewarded] here. [Customize]

There is a religious token here. When the token is brought to the statue, it causes the water to rise, making it possible to swim up to the passage at the green passage.

When the token is brought to the statue and offered, the PCs turn into merfolk, allowing them to breathe and maneuver easily underwater. It also allows them to pass through the southern passage to room 13.

11

In this chamber is another shrine and part of the ritual, as well as small glass pockets in the ceiling. Based on the murals, it appears these pockets are to let the divine sunlight enter into the chamber, though now at night only tiny slivers of moonlight are starting to peek through. The murals describe the heretics that rejected their merfolk form, who were punished by the Great Spirit of the Sun. Some managed to trick the spirit with deceit and sacrilege, and were banished to suffer on the surface for eternity.

The PCs can attempt to break the ritual in this room, but if they do they'll be attacked by a Drowned Maiden who is incorporeal and can only be permanently killed in physical form, and only takes physical form in moonlight.

12

There are twin alcoves, each one containing a standing suit of armor wrapped with dark stains. Each suit of armor clutches a pike that's shaped like a fey's head. A deathly silence fills the room. Shattered glass and the remains of shattered tables cover the floor in the dry section of the room. 15 feet ahead, arched doorways lead west and east from each side of the hallway. In each arched doorway, a bronze door stands closed.

In this room is a trap. A door or chest is rigged to activate when opened, which makes the trap swing out from a hole in the ceiling, toppling anyone in its path.

Effect: Targets all creatures within a 10 ft. square area, DC 15 DEX save or take 19 (4d10) damage and be knocked prone

Trigger: door, activates when a door or chest is opened.

Countermeasures: The DC to spot the attached wire is 20. A successful DC 15 Dexterity check using thieves' tools breaks the wire attached to the door harmlessly. A character without thieves' tools can attempt this check with disadvantage using any edged weapon or edged tool. On a failed check, the trap triggers.

[Customize]

The PCs find carvings and hieroglyphics along the walls of room 12 and 13. If they stop to read them, they'll discover that they depict the merfolk civilization's history, where it describes a sacred ritual that turned them into merfolk and allowed them to live under the water. The history describes the final step of the ritual to be bathed in the light of the rising sun, making the transformation into merfolk permanent.

13

This 35-foot-square room is in chaos. The area is spread with well-gnawed bones, smashed coral, and droppings. The mouth of a side chamber leads into blackness beyond. A black archway leads out through the west wall.

There are 1 Giant Water Beetle (CR 1/2: Fifth Edition Foes p. 25), 2 Zoblin (CR 1/4: Nerzugal's Extended Bestiary p. 96), 2 Sahuagin Priestess (CR 2: Monster Manual p. 264) [Easy, 1,100 XP rewarded] here. [Customize]

In the north passage (green) is a passage that dips down into a pool of water, then becomes a vertical cliff with a passage far above.

To The Surface

When the spirit is defeated it utters a curse as it vanishes, "heretics! Begone, I banish you from this place and relinquish your gift! Go, dry out and suffer on the surface for all eternity!"

Afterwards, if the PCs return to the surface they will transform back to their original forms. They'll also find a scar on their neck where their gills used to be.

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